The invention concerns fiber optic units, for example fiber optic couplers and multiplexers. For these and similar fiber optic units, the delicate nature of the fiber optic components makes them susceptible to damage in environments where their use is desired. Examples of the many environmental conditions that may affect the units are high hydrostatic pressure, substantial shock or vibration, high or low temperature, wide temperature variation, high humidity, corrosive environment, etc. It is desirable to find an inexpensive way to make fiber optic units in a form suitable for the particular conditions of the desired use and still achieve small exterior dimensions. It is likewise desirable to find a way to provide protective packaging of the unit in a manner that facilitates the handling of the components and permits their automated manufacture and assembly.